There have been proposed various kinds of a light receiving member for use in electrophotography. Among such known light receiving members, the public attention is now focused on such light receiving members having a photoconductive layer formed of an amorphous material containing silicon atoms as the main constituent atoms (hereinafter referred to as "A-Si") as disclosed in unexamined Japanese Patent Publication Sho. 54(1979)-86341 and Sho. 56(1981)-83746 since said photoconductive layer has a high Vickers hardness in addition to having an excellent matching property in the photosensitive region in comparison with that in other kinds of light receiving member and it is not harmful to living things as well as man upon the.
In concrete terms, said light receiving members have a photoconductive layer constituted with an A-Si material containing hydrogen atoms(H) and halogen atoms(X) [hereinafter referred to as "A-Si(H,X)"] and a surface layer being laminated on said photconductive layer which is constituted with a high-resistance amorphous material capable of allowing the transmittance of the light to be used, which serves as a layer to effectively prevent the photoconductive layer from being injected by electric chargein the electrification process and which also serves as a layer to improve the humidity resistance, deterioration resistance upon repeating use, breakdown voltage resistance, use-environmental characteristics and durability of the photoconductive layer.
There have been made various proposals on such surface layers to be disposed on a photoconductive layer of a light receiving member which exhibit the above mentioned functions for the photoconductive layer.
And among those known surface layers, a surface layer constituted with an A-Si(H,X) material containing at least one kind atoms selected from carbon atoms(C), oxygen atoms (O) and nitrogen atoms(N) [hereinafter referred to as "A-Si(C,O,N)(H,X)"] in a relatively small amount is generally evaluated as being the most preferred.
However, for the light receiving members having any of the known surface layers, even if it is the one that has such preferred surface layer as above mentioned, there are still unsolved problems particularly regarding the allowances for the kind of an usable light source and obtaining high quality images at high speed.
That is, firstly, it is extremely difficult to efficiently and to mass-produce the foregoing preferred surface layer having a uniform thickness and a stable film quality. The resultant surface layer will often become such that lacks uniformity of thickness and homogeneity of composition.
In addition, in any case, the light receiving member having such surface layer is to be repeatedly used, for instance, as in the case of an electrophotographic copying system. In that event, the surface layer will be gradually rubbed out by the mechanical actions of a copying sheet, toner, image developing device, cleaner etc. while being subjected to a locally partial abrasive force to thereby result in becoming uneven in thickness. These problems relative to the layer thickness of the surface layer will often bring about a local unevenness in the reflectivity of a light receiving member where there exists an interface between the surface layer and the photoconductive layer such that reflection of light is caused. This leads to making the light receiving member defective in photosensitivity and as a result, the images to be formed will be of an uneven image density which is a serious problem in electrophotography.
Further, as it is required for the above surface layer to be highly resistive in certain respects, there will be occasions which invite generation of residual voltage in the case of using the light receiving member repeatedly, particularly at high speed. In that case, there will be caused a problem that because of said residual voltage, the image quality will be reduced with the progress of the repeating use of the light receiving member. When using the light receiving member repeatedly for a long period of time, there will be another problem relative to the surface layer that its function to serve as a layer to prevent the occurrence of defective images will be gradually reduced to thereby invite the occurrence of defective images.
Further, there are still other problems for such light receiving members having the foregoing surface layer. That is, there will sometimes be such occasion that reflected ray occurs on the surface of the surface layer and another reflected ray occurs at the interface between the surface layer and the photoconductive layer being situated thereunder. In that case, the reflectivities of those reflected rays will be sometimes largely changed in accordance with the wavelength of the reflected ray, the layer thickness of the surface layer and the refractive index of the surface layer that results in bringing about unevenness in the color sensitivity of the photoconductive layer and in making the resultant images to be of uneven density.
The above problems relative to the surface layer were not serious and could be disregarded for the conventional ordinary-speed electrophotographic copying system but they are weighty problems which need to be settled in order for such light receiving members to be made effectively usable in high-speed continuous image-making systems such as a high-speed electrophotographic copying system using a coherent light laser beam as the light source, high-speed facsimile system and high-speed printer system and especially, in digital high-speed in a continuous image-making system.
There have been made the following proposals in order to solve the foregoing problems based upon eliminating relected ray at the interface between the surface layer and the photoconductive layer by adjusting the refractive index of the surface layer and that of the photoconductive layer at the interface: (a) a to make the composition of the surface layer to be closely resemble to or to be equivalent to that of the photoconductive layer at the interface between the two layers, (b) to make the optical band gap of the surface layer to be large enough in view of making light to be effectively impinged into the photoconductive layer and (c) a combination of (a) and (b).
However, any of these methods is not reliable to obtain such a desired light receiving member that can sufficiently satisfy the requirement for the high-speed continuous image-making systems, and there are still left some problems to be solved, which are chiefly directed to residual images and sensitivity related problems likely due to photocarriers to be generated as a result of the occurrence of light absorption at the interface between the surface layer and the photoconductive layer.
Against this background, digital high-speed continous image-making systems gradually have come into wide use. And there is an increased social demand for providing a desirable light receiving member which can sufficiently satisfy the requirements for such digital high-speed continuous image-making systems and which can stably exhibit the desired functions as the light receiving member for said systems.